1. Field of the Invention
The present invention relates to an optical apparatus such as a galvanometer mirror actuator or the like for rotationally driving an optical member to reflect or diffractively deflect light.
2. Related Background Art
In recent years there have been increasing needs for the machining technology for scanning with a light beam, such as a laser or the like, or for positioning it with high accuracy to utilize the laser energy such as in a laser marker or a stereo lithography device, and there are also known devices for deflecting a laser beam at high speed to draw an image, such as laser displays.
These devices are arranged to rotationally drive an optical member such as a reflection mirror or a diffraction grating to deflect or move the optical axis of the beam to a desired position, and various galvanometer mirror actuators may be used as driving devices for rotationally driving the optical member. Among these galvanometer mirror actuators, there are actuators for rotationally rocking the optical member only in a certain angular range according to use, and there are increasing demands for higher drawing or positioning accuracy and for quicker operation performance.
A conventional galvanometer mirror actuator has the structure as illustrated in FIGS. 5A, 5B to FIG. 7. In FIGS. 5A, 5B to FIG. 7, a reflection mirror 101 is supported on a plate spring 102 held on a base member 105 so as to be rotatable via neck portions 102a of the spring 102, and a pair of magnets 103 and a yoke 104 are attached to the lower surface of the reflection mirror 101. The magnets 103, together with the yoke 104 and base member 105, constitute a magnetic circuit. Attached to the base member 105 is a coil 106 for rotationally driving the reflection mirror 101 in cooperation with the magnets 103.
In this structure, when a current is supplied to the coil 106, a rotation movement is generated to twist the neck portions 102a of the plate spring 102 supporting the reflection mirror 101 to rotate the reflection mirror 101, thereby deflecting a beam incident to the reflection mirror 101. The center of rotation at this time is a point P in the neck portions 102a of the plate spring 102 as illustrated in FIG. 7.
In addition to the above structure, there are also known galvanometer mirror actuators using antifriction bearings such as ball bearings or the like as holding and rotation guiding means for the reflection mirror.
The conventional galvanometer mirror actuators described above, however, have the following issues to be solved.
(1) In the galvanometer mirror actuators having the structure for supporting the driven part by the plate spring, because the neck portions of the plate spring have a certain width, variations in the width and plate thickness make it hard to define the center of rotation of the driven part at a predetermined position. Since the plate spring undergoes twist deformation, the rigidity thereof is also degraded in directions except for the twist rotation directions. If the center of gravity of the driven part moves during the rotation because of the degradation of rigidity, the center of rotation will also move under the influence thereof, so as to produce such errors as an angular error of the reflected beam, offset deviation thereof, and so on, thereby degrading the positioning performance.
(2) In the galvanometer mirror actuators having the structure for supporting the driven part by antifriction bearings, while the radial rigidity can be kept high, continuous execution of fine feed operations will induce a shift in the positional relation between balls and a retainer of the bearing to increase a rotational friction torque suddenly, thereby degrading controllability. Since continuous execution of rotational rocking operations in a fixed angular range will bring about local deficiency of oil film in the bearing and tend to damage the bearing, this structure will need an oil feeding mechanism, periodic oil feeding, etc. and the apparatus will increase its scale and necessitate maintenance.